Blue phosphor for fluorescent display and method for synthesizing the same

ABSTRACT

Provided are a blue phosphor for a fluorescent display having a high luminous efficiency, and a method for synthesizing the same. The blue phosphor is obtained from a host composed of strontium carbonate (SrCO 3 ) and an activator composed of a cerium compound. The method for synthesizing the blue phosphor includes preparing a mixture having strontium carbonate (SrCO 3 ) and a cerium oxide (CeO 2 ) homogenously mixed according to the composition having the following general formula:  
     SrCO 3 +xCeO 2    
     wherein 0.01° x° 0.5, and annealing the mixture at 800 to 900°Δ C.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to display technology, and moreparticularly, to a blue phosphor for a fluorescent display and a methodfor synthesizing the same.

[0003] 2. Description of the Related Art

[0004] Fluorescent displays, in particular, field emission displays(FEDs) are flat-panel displays driven by the same operating principle ascathode ray tubes (CRTs), and are constructed such that a cathode plate,which is a field emitter array (FEA) panel emitting electrons by anelectric field rather than by thermions, and an anode plate, which is afluorescent panel receiving electrons to emit light, are a predeterminedgap spaced apart and packaged in high vacuum state.

[0005] Conventional CRTs generally employ sulfide-based phosphors whichare good in color purity and luminous efficiency. However, if FEDs, inwhich a space between a cathode plate and an anode plate is short, use ahigh voltage of 10 kV or greater like in CRTs, discharge occurs. Thus,FEDs use a low voltage of 5 kV or less. In particular, in order todevelop FEDs operable at a voltage as low as 1 kV or less, variousresearches are globally being carried out.

[0006] However, if the electronic energy is as low as 1 kV or less,electrons can only be scanned as deep as 20 nm from a phosphor surface.Thus, the efficiency, particularly luminescence, of a phosphor for alow-voltage operating FED is considerably lower than a CRT operating ata high voltage. Also, the surface state of a phosphor greatly affect theluminous efficiency thereof.

[0007] In particular, when a conventional sulfide blue phosphor, ZnS:Ag, Al, which has been widely used in CRTs, is used as an FED phosphor,it exhibits bad luminous efficiency and color purity at low voltages.Also, prolonged E-beam scanning gives rise to desorption of a trace ofsulfur from sulfide-based phosphors, resulting in a decrease in theinternal vacuum degree for smaller volume in the case where the distancebetween a cathode plate and an anode plate is approximately 1 mm like inan FED panel or impairing an FEA, thereby deteriorating displayperformance. To address such problems, vigorous research intooxide-based phosphors free from the risk of desorbing sulfur therefromhas recently been made.

[0008] For variety of applications, there is increasing demand forphosphors capable of exhibit high luminescence at low production cost.In order to reduce the production cost, not only the source materialcost but also the processing cost required for manufacturing phosphorsmust be low. In current actuality, the major factor in the processingcost is the annealing temperature in the course of synthesis. Under thecircumstances, in order to obtain low-cost phosphors, it is quiteimportant to synthesize highly luminescent phosphors that can besynthesized at a low annealing temperature.

SUMMARY OF THE INVENTION

[0009] To solve the above problems, it is an object of the presentinvention to provide a blue phosphor for a fluorescent display, whichhas a high luminous efficiency at low voltages and can be synthesized ata low annealing temperature without desorption due to prolonged E-beamscanning.

[0010] It is another object of the present invention to provide a methodfor synthesizing a blue phosphor for a fluorescent display, which has ahigh luminous efficiency at low voltages and can be synthesized at a lowannealing temperature without desorption due to prolonged E-beamscanning.

[0011] To achieve the first object, the present invention provides aphosphor for a fluorescent phosphor blue phosphor for a fluorescentdisplay obtained from a host composed of strontium carbonate (SrCO₃) andan activator composed of a cerium compound.

[0012] The cerium compound is preferably a cerium oxide (CeO₂), and thehost and the activator are preferably mixed in a molar ratio of1:0.01˜1:0.5.

[0013] To achieve the second object, the present invention provides amethod for synthesizing a blue phosphor for a fluorescent display,including preparing a mixture having strontium carbonate (SrCO₃) and acerium oxide (CeO₂) homogenously mixed therein, and annealing themixture.

[0014] The strontium carbonate (SrCO₃) and the cerium oxide (CeO₂) arepreferably mixed according to the composition having the followinggeneral formula:

SrCO₃+xCeO₂

[0015] wherein 0.01°

x°

0.5

[0016] Preferably, the strontium carbonate (SrCO₃) and the cerium oxide(CeO₂) are mixed in a molar ratio of 1:0.05.

[0017] Here, annealing is preferably performed at approximately 800°Δ C.to approximately 900°Δ C. for approximately 12 to approximately 36hours.

[0018] According to the blue phosphor of the present invention, when itis applied to a fluorescent display or used as an anode plate of an FEDphosphor, it can prevented from being destructed due to prolongedscanning time so that the degree of vacuum between the cathode plate andthe anode plate can be maintained, thereby maintaining the panelperformance for a long time of period. Also, since the synthesistemperature of the blue phosphor for a fluorescent display according tothe present invention is lower than that of the conventional phosphor,the production cost can be remarkably reduced while exhibiting highluminescence. Therefore, when the blue phosphor according to the presentinvention is applied to a fluorescent display, it can exhibit goodcharacteristics such as high luminescence or high definition and canmake a large contribution to commercialization of low voltage FEDs.

BRIEF DESCRIPTION OF THE DRAWING

[0019] The above objective and advantages of the present invention willbecome more apparent by describing in detail preferred embodimentsthereof with reference to the attached drawing in which:

[0020]FIG. 1 is a flow chart for explaining a method for synthesizing ablue phosphor for a fluorescent display according to a preferredembodiment of the present invention;

[0021]FIG. 2 is a photoluminescence (PL) emission spectrum of the bluephosphor for a fluorescent display according to a preferred embodimentof the present invention;

[0022]FIG. 3 is a PL excitation spectrum of the blue phosphor for afluorescent display according to a preferred embodiment of the presentinvention;

[0023]FIG. 4 is a graph showing the PL intensity of excitation spectrum(emission wavelength=470 nm) of the blue phosphor for a fluorescentdisplay according to a preferred embodiment of the present invention,the PL intensity depending on a change in x; and

[0024]FIG. 5 is an X-ray diffraction spectrum depending on annealingtemperature of the blue phosphor for a fluorescent display according toa preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025]FIG. 1 is a flow chart for explaining a method for synthesizing ablue phosphor for a fluorescent display according to a preferredembodiment of the present invention.

[0026] Referring to FIG. 1, a mixture having strontium carbonate (SrCO₃)as a host and cerium oxide (CeO₂) as an activator homogenously mixed isprepared (step 10). To this end, strontium carbonate (SrCO₃) and ceriumoxide (CeO₂) are put into a mortar containing alcohol as a solventaccording to the composition having the following general formula,followed by homogenously mixing and drying:

SrCO₃+xCeO₂

[0027] wherein 0.01°

x°

0.5.

[0028] Preferably, SrCO₃ and CeO₂ are mixed in a molar ratio of 1:0.05.

[0029] Thereafter, the resultant dried mixture obtained in step 10 isput into an alumina tube and annealed at an electric heater maintainedat a temperature of approximately 800 to 900°Δ C. for approximately 12to 36 hours, thereby synthesizing a desired phosphor (step 20).

[0030] If the annealing temperature exceeds 1000°Δ C., different phasephosphors are generally synthesized. In particular, a sample annealed at1000°Δ C. is chemically instable so that it easily reacts with CO₂ orH₂O under the atmospheric condition. However, according to the presentinvention, the blue phosphor is synthesized at a relatively lowtemperature of approximately 800 to 900°ΔC.

[0031] Therefore, the production cost of phosphors capable of exhibitinghigh luminescence can be greatly reduced.

[0032]FIG. 2 is a photoluminescence (PL) emission spectrum of the bluephosphor for a fluorescent display according to a preferred embodimentof the present invention. In detail, samples having the general formulaSrCO₃+xCeO₂ (x=0.01, 0.05, 0.1, 0.33, 0.4 and 0.5) are annealed at 800°ΔC. under the atmospheric condition for 12 hours, yielding powder of thephosphor according to the present invention, and then PL properties ofthe powder are evaluated. The results are shown in FIG. 2. Referring toFIG. 2, when x=0.05, the luminescence is highest. The wavelength atwhich the PL intensity is maximum is 470 nm, and the powder emits blueradiations.

[0033]FIG. 3 is a PL excitation spectrum of the blue phosphor for afluorescent display according to a preferred embodiment of the presentinvention. In detail, samples having the general formula SrCO₃+xCeO₂(x=0.01, 0.05, 0.1, 0.33, 0.4 and 0.5) are annealed at 800°Δ C. underthe atmospheric condition for 12 hours, yielding powder of the phosphoraccording to the present invention, and PL excitation spectralproperties of the powder are shown in FIG. 3. Referring to FIG. 3, twobands are shown according to x value. When x=0.05, the luminescence ishighest.

[0034]FIG. 4 is a graph showing the PL intensity of excitation spectrumof the blue phosphor for a fluorescent display according to a preferredembodiment of the present invention, the PL intensity depending on achange in x. In detail, samples having the general formula SrCO₃+xCeO₂(x=0.01, 0.05, 0.1, 0.33, 0.4 and 0.5) are annealed at 800°Δ C. underthe atmospheric condition for 12 hours, yielding powder of the phosphoraccording to the present invention, and then PL intensities thereof aremeasured according to a change in x value, when the emission wavelengthis 470 nm. Referring to FIG. 4, when x=0.05, the luminescence ishighest.

[0035]FIG. 5 is an X-ray diffraction spectrum depending on annealingtemperature of the blue phosphor for a fluorescent display according toa preferred embodiment of the present invention. In detail, sampleshaving the general formula SrCO₃+xCeO₂ (x=0.01, 0.05, 0.1, 0.33, 0.4 and0.5) are annealed at 800°Δ C. under the atmospheric condition for 12hours, yielding powder of the phosphor according to the presentinvention, and then X-ray spectrums thereof are shown in FIG. 5.Referring to FIG. 5, main peaks of the sample powder annealed at 800°ΔC. indicate SrCO₃ and some peaks indicate Sr(OH)₂. In the sample powderannealed at 900°Δ C., main peaks indicate SrCO₃ and some peaks indicateSr₂CeO₄.

[0036] The blue phosphor for a fluorescent display according to apreferred embodiment of the present invention is obtained from a hostcomposed of strontium carbonate (SrCO₃) and an activator composed ofcerium oxide (CeO₂), and it is synthesized at a relatively low annealingtemperature. The blue phosphor for a fluorescent display according to apreferred embodiment of the present invention is an oxide phosphor whichis stable to thermal stimulus or other external stimuli such as E-beamscanning. Thus, when the (SrCO₃+CeO₂) oxide phosphor according to thepresent invention is applied to a fluorescent display or an anode plateof an FED phosphor, destruction thereof due to prolonged E-beam scanningcan be prevented, so that the degree of vacuum of a space between acathode plate and an anode plate is maintained, thereby maintainingpanel performance for a long time of period. Also, since the phosphorfor a fluorescent display according to the present invention has a verylow synthesis temperature in the manufacture process compared toconventional phosphors, the production cost thereof can be remarkablyreduced. Therefore, when the phosphor for a fluorescent displayaccording to the present invention is applied, it can exhibit goodproperties including high luminescence or high definition. Also, thephosphor for a fluorescent display according to the present inventioncan make a large contribution to commercialization of low-voltage FEDs.

[0037] While this invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A blue phosphor for a fluorescent displayobtained from a host composed of strontium carbonate (SrCO₃) and anactivator composed of a cerium compound.
 2. The blue phosphor of claim1, wherein the cerium compound is a cerium oxide (CeO₂).
 3. The bluephosphor of claim 1, wherein the host and the activator are mixed in amolar ratio of 1:0.01˜1:0.5.
 4. The blue phosphor of claim 2, whereinthe host and the activator are mixed in a molar ratio of 1:0.01˜1:0.5.5. A method for synthesizing a blue phosphor for a fluorescent display,comprising: (a) preparing a mixture having strontium carbonate (SrCO₃)and a cerium oxide (CeO₂) homogenously mixed therein; and (b) annealingthe mixture.
 6. The method of claim 5, wherein in step (a), thestrontium carbonate (SrCO₃) and the cerium oxide (CeO₂) are mixedaccording to the composition having the following general formula:SrCO₃+xCeO₂ wherein 0.01°

x°

0.5.
 7. The method of claim 6, wherein the strontium carbonate (SrCO₃)and the cerium oxide (CeO₂) are mixed in a molar ratio of 1:0.05.
 8. Themethod of claim 5, wherein in step (b), annealing is performed at 800°ΔC. to 900°ΔAC.
 9. The method of claim 5, wherein in step (b), annealingis performed for 12 to 36 hours.